The invention relates in general to electric motor/gear drive systems and in particular to electric motor/gear drive systems for use in areas with limited space.
Electric motors have been widely used to power machinery. Electric motors are matched to gear drives, belts, chains, and other multipliers to provide more torque. In an environment where space and weight is limited, the need for packaging efficiency (overall size) is a critical factor in the ultimate solution to a torque multiplier problem.
Traditional mounting of the electric motor is to the input face of the gearbox. Gearboxes are generally constructed in an inline or right angle configuration, or use chain, belt, worm, or gear drives to transfer motion from a motor to the gearbox. If there are limitations in the available space in the output axis direction, an inline motor/gearbox may be too long. Compared to an inline gearbox, a right angle gearbox will shorten the output axis distance but will add to the space claim in the transverse axes. And, the right angle gearbox requires the addition of a gear set (i.e. bevel) to accomplish the change in direction of motion, which will usually limit the torque capacity of the drive. Higher torque capacity drives may require more space, increase the overall system weight, and have a lower efficiency (for example, worm drives).
Packaging of a parallel, over-and-under type arrangement between the gearbox and electric motor will provide a short space claim along the output shaft axis, but requires the addition of a transfer mechanism of some type (chain, belt, gears, etc.). Depending on the torque and speeds of the drive, the transfer mechanism can add significant weight and space claim, along with an increase in friction losses.
With respect to the electric motor, brushless DC servo motors have a greater power density (defined as torque output relative to volume of motor) in a large diameter/short axial length configuration than in a small diameter/long axial length configuration. To gain the required torque output of a servomotor in the more traditional small diameter/long axial length configuration, the axial length can become prohibitive. In traditional systems, the motor is mounted directly to the input face of the gearbox, resulting in a cantilevered load that is borne by the gearbox structure and mounting. In high g-loaded environments (high acceleration), the cantilevered load can put significant forces into the gearbox. These forces may require the use of a larger frame size configuration than usually needed for a given torque output, thereby increasing the weight and space claim of the drive system.